The present invention relates to an intervehicular alarm system and an intervehicular alarm apparatus, and particularly to a technique for transmitting and receiving alarm information between vehicles by using light, radio waves and the like.
Conventionally, techniques for transmitting alarm information to other vehicles by radio have been proposed. For example, Japanese Patent Laid-open No. Hei 1-202549 discloses a configuration in which a radio apparatus is included in a vehicle to allow alarm sound from another vehicle to be reliably perceived by a driver even when an audio apparatus is used in the vehicle, an alarm signal of a specific frequency is transmitted when an alarm switch is turned on, and alarm speakers are driven when the alarm signal is received from the outside.
However, when thus transmitting and receiving an alarm signal by radio, a vehicle other than the one for which the alarm signal is originally intended also receives the alarm signal as long as the vehicle is within reach of the radio, and the vehicle on receiving the alarm signal issues an alarm from speakers even though the transmitting vehicle is not present in the vicinity of the receiving vehicle. Thus, the driver of the receiving vehicle is confused.
Of course, it is conceivable that the reach of the radio may be limited to a certain range, but this may result in a case where an alarm does not reach a vehicle to which the alarm signal is originally intended to be transmitted.
In addition, even if the intended vehicle receives the alarm signal, it is difficult for the driver of the vehicle to determine the direction from which the alarm is issued when the alarm is simply outputted from speakers. The driver therefore needs to identify the vehicle that has issued the alarm by looking around when the alarm has been issued.